The present invention relates to materials having a fluorescent marker. More particularly, the invention relates to a synthetic polymer having a near infrared fluorophore associated with the polymer. Another aspect of the present invention is a method for incorporating a thermally stable fluorescing marker into cellulose acetate.
The incorporation of an invisible marker into or onto a natural or synthetic material has recently acquired an elevated awareness due to a variety of reasons. Primarily, such markers have found great utility in security measures for documents, such as checks, passports, negotiable instruments, stock certificates and the like, and labels for pharmaceuticals, health care and cosmetics. Markers have also been incorporated into fibers and threads for woven, nonwoven and knitted materials, as well as being placed on a garment as a means for verifying its authenticity. For example, in the clothing industry, the prevention of counterfeited articles is necessary to protect profitability, assure the customer of the quality of the goods sold, and protect the brand name and loyalty of the customer. The marking of authentic articles is only one means used to achieve these, as well as other, goals of the producer.
Use of fluorescent agents for the tracing and identification of articles such as monitoring the integrity of the yarn or fiber during slashing, warping or weaving is described in U.S. Pat. No. 4,992,204. The patent discloses tagging a material with a luminophore that is cross-linked with at least one poly(oxyalkylene). The tagging compound has an absorbance within the range of about 300 nm to 400 nm.
U.S. Pat. No. 4,504,084 issued to Miehe et al. on Nov. 12, 1991 discloses a method for marking originals so that copies can be distinguished from the originals. The method includes using a ribbon having a printing medium for printing the original. The ribbon includes a substance in the form of a marking which, when used, produces an invisible distinguishable marking which is recognizable only by using a special scanner.
Fluorescing markers have also been used in the petroleum and plastics industry as a means for identifying the material and/or separating marked materials from non-marked materials. For example, U.S. Pat. No. 5,525,516 teaches a method for marking or tagging petroleum products such as diesel fuel, gasoline, and the like with a near infrared fluorescing marker. Such marked petroleum products may then be readily identified.
U.S. Pat. Nos. 5,397,819, 5,553,714 and 5,461,136 teach incorporating a near infrared fluorescing compound into thermoplastic materials. The general concept of tagging various thermoplastic materials with near infrared fluorophores for identification purposes is disclosed in U.S. Pat. No. 5,397,819. This patent relates to a method for marking or tagging a thermoplastic polymeric material using conventional techniques such as those employed to incorporate other additives in similar resins, such as, by admixing, dry or melt blending as powders or pellets, or copolymerizing one or more thermally stable, near infrared fluorescing compounds therein. A wide range of thermoplastic polymers are suitable for blending with the near infrared fluorophore including polyesters such as poly(ethylene terephthalate) and poly(butylene terephthalate); polyolefins such as polypropylene, polyethylene, linear low density polyethylene, polybutylene and copolymers made from ethylene, propylene and butylene; polyamides such as nylon 6 and nylon 66; polycarbonates; cellulose esters such as cellulose acetate, propionate, butyrate, or mixed ester; polyacrylates such as poly(methyl methacrylate); polyimides; polyester-amides; polystyrene; ABS (acrylonitrile-butadine-styrene) type polymers, and thermoplastic oligomers, and the like.
When the near infrared fluorophore is melt blended into the polymer, these operations are conducted at temperatures in excess of 200.degree. C., frequently in excess of 250.degree. C. At such high temperatures, the near infrared fluorophores are readily blended in the molten polymer melt during preparation or processing or just prior to molding or spinning into a fiber and remain in the polymer as true a true blend after processing.
However, it has been discovered that the thermally stable near infrared fluorophores used for this purpose do not readily associate with cellulose esters under the mild conditions required for processing these materials. Most cellulose esters are relatively thermally unstable, requiring them to be processed at temperatures below about 200.degree. C. Under these relatively mild process conditions, the near infrared fluorophores do not dissolve or disperse in the material, nor do the near infrared fluorophores dissolve or disperse into the ordinary plasticizers or solvents used in manufacturing cellulosic esters. The result can be dispersed pockets of fluorescing compounds. These undistributed compounds can further adversely affect the properties of the thermoplastic or articles made from them. Consequently, it has not been possible heretofore to feasibly and acceptably incorporate these thermally stable near infrared fluorophores in cellulosic esters.
Accordingly, there is a need for a cellulosic ester having at least one near infrared fluorophore associated with the thermoplastic. There is also a need for a method of associating a thermally stable near infrared fluorophore with a cellulosic ester.